JP2002077735A - Solid-state image pickup element and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize blooming characteristic measurement, etc., with a single image pickup device without receiving influence from discrimination error caused by the flare in an optical system. SOLUTION: In the two-dimensional pixel array of a CCD image pickup element 105, an optical black(OB) area is provided. In order to make the various characteristics of the image pickup element 105 measurable, a dummy white section is installed on a partial line of the OB region. The dummy white section is a pixel raw which can read out accumulated charges without inputting light and each pixel is connected with a current source for injecting charges. A system controller 112 can detect the influence of leakage charges from the dummy white section by evaluating the output signal from the OB area. Therefore, the image pickup device can easily measure blooming characteristics without inputting light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state image sensor such as a CCD and an image pickup apparatus for picking up a subject image using the same.

[0002]

2. Description of the Related Art Imaging devices using solid-state imaging devices such as CCDs are widely used. On the other hand, a solid-state image sensor generally has pixel defects, and may generate false signals such as dark current, smear, color mixing due to blooming or transfer failure, and the driving conditions are managed so that these are unlikely to occur. By improving the performance substantially by adopting a technique for correcting the generated pseudo signal or the pseudo signal, practical use can be realized at low cost.

A typical example of such a technique is an OB (optical black = optical black) provided in an image sensor. That is, a light-shielding portion is provided in a part of the pixel in the photoelectric conversion region, and the dark charge level is detected by always setting the pixel to have a photoelectric charge of 0, and the detected dark charge level is reduced from the normal photosensitive pixel signal output other than OB. This corrects the effect of the dark current of the photocharge storage unit. Since the above-described subtraction is usually performed by a clamp circuit, O
It is called B clamp.

[0004]

The dark current can be corrected by providing an OB in the image pickup device and performing the OB clamp, but there is another problem which cannot be solved by this. For example, there is an optimal setting of a clip level (= saturation level) in a pixel.

[0005] In other words, the saturation level of the photoelectric conversion unit is the overflow level of the storage unit, and even if a photoelectric charge exceeding this level is generated, it is discharged to the overflow drain and is not accumulated. Such a mechanism is provided in order to prevent the image quality deterioration due to the overflow of the excess electric charges = blooming, and the overflow level OFL is provided.
Can be varied by a set value of a substrate bias voltage VSUB described later. However, if the OFL is too high, blooming tends to occur. Therefore, the OFL is usually set to be as high as possible within an allowable limit of blooming characteristics. is there.

In order to determine the permissible limit on the blooming characteristics, it has conventionally been necessary to actually make light incident on the image sensor. For example, a method has been used in which a spot-shaped bright spot chart is photographed, and whether or not the output does not leak into the surrounding dark area is used. The problem is that this is a time-consuming process that itself requires special settings, and therefore also incorporates into the user's environment, for example, a camera self-diagnosis function that runs immediately after power on. I couldn't do anything. Furthermore, there is a risk of erroneous determination due to flare depending on the optical system used.

The present invention has been made in consideration of the above circumstances, and has as its object to easily evaluate various characteristics without requiring an optical input. Therefore, for example, an error caused by the influence of a flare of an optical system. An object of the present invention is to provide a solid-state imaging device capable of performing blooming characteristic measurement or the like with an imaging device alone without fear of determination and an imaging device using the same.

[0008]

In order to solve the above-mentioned problems, a solid-state image pickup device according to the present invention has a two-dimensionally arranged charge storage section configured as a pixel in a photoelectric conversion region for photoelectrically converting a subject image. A two-dimensional pixel array, an imaging signal readout unit that reads out charges stored in the two-dimensional pixel array, and a pixel unit assigned to at least a part of the two-dimensional pixel array. A dummy white portion having current source means for inputting a significant charge even when there is no photocharge input to the portion.

By providing a dummy white portion having a current source means in a part of the two-dimensional pixel array, a predetermined pixel charge can be obtained without giving light, so that various characteristics can be easily evaluated. can do.

Preferably, the dummy white portion is provided adjacent to an optical black OB (optical black) region in a two-dimensional pixel array. As a result, it is possible to detect the influence of the leakage of the electric charge from the dummy white portion only by evaluating the output signal from the OB region.
The blooming characteristics can be easily measured without giving light.

It is preferable that the dummy white portion is provided at an end of the two-dimensional pixel array. Thereby, the arrangement of the current source means can be realized very easily.

Further, the present invention is an image pickup apparatus comprising the solid-state image pickup device according to any one of claims 1 to 3, wherein the solid-state image pickup device picks up a subject image using the solid-state image pickup device. And a saturation level detecting means for detecting a saturation level of a photoelectric conversion region of the solid-state imaging device based on an output signal from the dummy white portion. As described above, by providing a means for detecting the saturation level using the output signal from the dummy white portion in the imaging device, the saturation level can be detected by the imaging device alone without giving light, and the clip level of the pixel can be detected. Can be easily realized.

The image pickup apparatus using a solid-state image pickup device according to claim 2, wherein the dummy white portion is provided adjacent to an optical black OB (optical black) region in the two-dimensional pixel array. It is preferable to provide a means for setting an overflow level of the solid-state imaging device based on an output signal from an optical black OB (optical black) region. With this configuration, it is possible to set the overflow level of the solid-state imaging device with the imaging device alone without giving light.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an imaging device according to an embodiment of the present invention. Here, a case where the present invention is implemented as a digital camera will be described as an example.

In FIG. 1, reference numeral 101 denotes an imaging lens system including various lenses; 102, a lens driving mechanism for driving the lens system 101; 103, an exposure control mechanism for controlling the aperture of the lens system 101; Optical filter for outer cut, 105 is CC with built-in color filter
D-color image sensor, 106 a CCD driver for driving the image sensor 105, 107 a pre-processing circuit including an A / D converter, and 108 a color signal generation process, a matrix conversion process, and various other digital processes. A digital interface circuit 109; a card interface 110; a memory card 110 for recording a captured image; and 111 an LCD image display system.

Further, in the figure, reference numeral 112 denotes a system controller (CPU) for comprehensively controlling each unit, 113 denotes an operation switch system including various SWs, and 114 denotes an operation display for displaying an operation state, a mode state, and the like. System, 115 is a lens driver for controlling the lens driving mechanism 102, 116 is a strobe as light emitting means, 117 is an exposure control driver for controlling the exposure control mechanism 103 and the strobe 116, and 118 is various kinds of setting information and the like. 1 shows a non-volatile memory (EEPROM) for performing the operation.

In the digital camera of the present embodiment,
The system controller 112 performs overall control, and controls the driving of the CCD image pickup device 105 by the CCD driver 106 to perform exposure (charge accumulation) and signal readout. After the image signal is taken into the digital process circuit 108 to generate an image signal for recording, the image signal is recorded on the memory card 110 via the card interface 109.

As the CCD image pickup device 105, an interline type CCD having a vertical overflow drain (VOFD) structure or the like is used. This CCD image sensor 105
Is controlled by various drive signals (charge transfer pulse TGP, vertical drive pulse,
Horizontal driving pulse, substrate voltage VSUB, etc.). The substrate voltage VSUB is a substrate bias voltage for determining the maximum charge accumulation level (overflow level OFL) of the charge accumulation section, and this VSUB is applied to the substrate by superimposing a large value pulse (SBP) on the substrate. It is also used for forced discharge of all charges. The VSUB variable setting is performed by a VSUB variable setting circuit 106a provided in the CCD driver 106. The VSUB variable setting circuit 106a is for setting the overflow level OFL by variably setting the value of VSUB under the control of the system controller 112, and includes, for example, a D / A converter and a buffer amplifier.

The two-dimensional pixel array of the CCD image pickup device 105 is provided with the above-described optical black OB (optical black) area. Further, in the present embodiment, C
In order to measure various characteristics of the CD imaging device 105, a dummy white portion is provided in a part of the line of the OB area. The dummy white portion is a pixel row from which stored charges can be read without light input, and a current source for charge injection is connected to each pixel. The system controller 112 includes a saturation level detection unit 112a and an overflow level setting unit 11 so that the characteristic measurement of the CCD image pickup device 105 can be realized by being incorporated into the self-diagnosis function of the digital camera.
2b is provided.

The saturation level detector 112a is for detecting the saturation level of the photoelectric conversion area of the CCD image sensor 105 based on the output signal read from the dummy white portion. The clip level of the signal is set. The overflow level setting unit 112b sets the overflow level OFL of each charge storage unit of the CCD image sensor 105 to the VSUB variable setting circuit 10
6a, based on the output signal read from the OB area adjacent to the dummy white portion so that the overflow level OFL is as high as possible within the allowable limit of the blooming characteristic. The optimum value of the overflow level OFL is determined.

FIG. 2 schematically shows the structure of the CCD image pickup device 105. As shown, the CCD image sensor 105 has a two-dimensional pixel array in which a plurality of pixels PXL (PD) including a photoelectric conversion region (charge storage unit) are two-dimensionally arranged. A horizontal transfer path (HCCD) is provided at one end of the two-dimensional pixel array, and a vertical transfer path (VCCD) is provided for each vertical pixel array. When the charge transfer pulse TGP is output, a transfer gate provided between the charge storage portion of each pixel (PXL) and the corresponding vertical charge transfer path (VCCD) opens, and the corresponding vertical charge is transferred from each charge storage portion. The charge is transferred to the transfer path (VCCD). Then, by the transfer driving of the vertical charge transfer path (VCCD) and the horizontal transfer path (HCCD), the charges accumulated in the two-dimensional pixel array are read out through an output amplifier (floating diffusion amplifier FDA: Floating Diffusion Amplifier).

In the two-dimensional pixel array, the horizontal transfer path (H
12 lines on the opposite side of the CCD) are pixels (PXL)
Are completely shielded from light, and form a vertical optical black VOB (optical black) region. In the VOB area, a constant current source is connected to the hatched pixel (PXL) in the outermost one line to form a dummy white portion (resulting in 11 VOB lines). The reason why the dummy white portion is provided at the end of the two-dimensional pixel array is to make the arrangement of the current source circuit extremely easy.

FIG. 3 shows a cross-sectional structure of an interline CCD having a vertical overflow drain structure, which is used as the image sensor 105 of the present embodiment. The n-type semiconductor substrate 400 has a first region 40 of a P-well having a shallow junction.
1 and a second region 402 of a P well having a deep junction. A portion of the first region 401 where the junction n-type region is formed is a photoelectric conversion region 403 including a photodiode (PD) and a charge storage portion, and functions as a pixel (PXL).

A buried channel 404 is provided in the second region 402.
Vertical shift register, ie, vertical transfer path (VCC
A transfer electrode 405 for D) is formed. On its main surface, a metal layer 409 is arranged via an insulating layer 406. The photoelectric conversion region 403 and the buried channel 404 are separated by a channel stop region 407 made of a high p-type impurity layer.

A transfer gate (T) is provided between the photoelectric conversion region 403 and the corresponding buried channel 404.
G) A region 408 is arranged. Further, the area other than the photoelectric conversion region 403 is shielded from light by the metal layer 409. In addition,
The VOB region and the dummy white portion are completely shielded from light including the photoelectric conversion region 403.

The blooming is suppressed by the N-type semiconductor substrate 400.
Bias voltage VSUB, which is a reverse bias voltage, at the junction between the first region 401 and the second region 402 of the P-well.
411 is applied to completely deplete the first region 401 of the P well immediately below the photoelectric conversion region 403 (depletion layer formation). In this case, photoelectrons (negative charges) are stored in the storage capacitor of the photoelectric conversion region, and the potential decreases (increases in negative), and a certain level (O) corresponding to the VSUB value is obtained.
The portion exceeding FL) is swept out to the substrate 400 over the potential barrier. Thus, OFL can be variably adjusted by VSUB. By applying a pulse (SBP) having a larger value than usual to VSUB, all the photoelectrons stored in the storage capacitor of the photoelectric conversion region are discharged to the substrate (forcible discharge of all charges).

FIGS. 4A and 4B are circuit diagrams respectively showing the pixel structure of the dummy white portion and the pixel structure of the other portion. As shown in FIG.
The constant current source IS is connected to the pixel (PXL) in the dummy white portion, and the other points are the same as the pixel structure of the other portion shown in FIG. Regarding the pixel (PXL) in the dummy white portion, a constant charge (negative charge) is accumulated by the action of the constant current source IS even in the light-shielded state.

In FIGS. 4A and 4B, for example, the symbol of the battery of OFL and the symbol of the diode merely indicate the function of the potential barrier described in FIG. 3, and the circuit element does not actually exist. In that sense, FIG. 4 is not an equivalent circuit of the cross-sectional structure of FIG. 3, but it is functionally equivalent thereto. In FIG. 4, the CP of the pixel (PXL)
Indicates the storage capacity of the photoelectric conversion area, and CV indicates the capacity of the vertical transfer path (VCCD) corresponding to each pixel (PXL).

As the constant current source IS in the dummy white portion, a known current mirror circuit as shown in FIG. 5 can be used. As described above, since the charge carriers of the CCD are electrons (negative charges), the circuit has a negative polarity (sinks current). However, if the charge carriers are positive charges, a positive polarity circuit may be employed. Needless to say. In the following, for simplicity, negative charge is omitted, and is simply referred to as charge or current supply.

In the current mirror circuit of FIG. 5, the same base current as that of the NPN transistor Q1 on the primary side flows through the bases of the NPN transistors Q2 to Qn + 1 on the secondary side, so that the NPN transistors Q2 to Q2 on the secondary side
The collector current of Qn + 1 can be made equal to the collector current of NPN transistor Q1 on the primary side. By connecting the collectors of the NPN transistors Q2 to Qn + 1 on the secondary side to the pixels of one line of the dummy white portion, the same current is supplied to all the pixels of the one line.

Next, the operation of setting the clip level (= saturation level) of the CCD image pickup device 105 having the above structure will be described. First, under the control of the system controller 112, a signal readout of pixel charges from the CCD image pickup device 105 is performed. In this case, the TBP
The accumulation time (current input time to the dummy white portion) determined by the period up to the output is selected as a time that is sufficiently saturated by the constant current i of the constant current source IS.

A read signal from each pixel is taken into a digital process 108 via an A / D converter. The system controller 112 controls the digital process 10
8 and the output signal (D
The W output) is analyzed using the saturation level detection unit 112a, and the saturation level (= clipping level) is determined. If the accumulation time corresponding to the saturation level is unknown, the DW output for each frame may be monitored while repeatedly changing the accumulation time, and it may be determined that the saturation has occurred when there is no change. The value of the saturation level detected in this manner can be used, for example, for setting the maximum input level of the A / D converter.

Next, referring to the flowchart of FIG.
The operation of setting the OFL will be described.

The operation of setting the OFL is performed in a state in which the accumulation time (current input time to the dummy white portion) is selected to be a time that is sufficiently saturated by the constant current i (as described above, the DW output is monitored every frame). , Thereby determining the accumulation time as a result). First, the overflow level setting unit 112b of the system controller 112
The VSUB voltage is initialized to an appropriate initial value (for example, 0) by using the VSUB variable setting circuit 106a (step S).
11). Then, the signal reading of the pixel charges from the CCD image pickup device 105 is repeatedly executed. The readout signal from each pixel is sent to the digital process 1 via the A / D converter.
08.

The overflow level setting unit 112b
The signal (OB output) for one line in the OB area adjacent to the dummy white portion is monitored every frame, and it is checked whether the OB output is affected by blooming from the dummy white portion (step S12). Initially, the VSUB voltage is low,
As a result, the overflow level is set high, so that OB has a significant output (N in step S12).
O). In this case, the overflow level setting unit 112b
Uses the VSUB variable setting circuit 106a to gradually decrease the overflow level by increasing the VSUB voltage in an appropriate resolution unit (step S13).
As VSUB increases, the overflow level decreases,
As a result, the adjacent OB output decreases. The adjacent OB output is 0
Is reached (YES in step S12), the adjustment is completed, and the value of VSUB at that time is written into the EEPROM 118, and the process is terminated (step S14).

At the time of the subsequent main image pickup, the EEPROM 118
The setting of the VSUB value, that is, the setting of the overflow level, is performed by using the stored value in the step (1), and in this state, the imaging operation synchronized with the shutter trigger is executed.

Note that the above-described operation of detecting the saturation level and O
The FL setting operation is incorporated as a self-diagnosis function of the digital camera. Further, in this example, only the operation of detecting the saturation level and the operation of setting the OFL have been described. However, various characteristics of the image sensor can be measured by using a signal from the dummy white portion. Furthermore, the control of the structure of the CCD image sensor 105 and the OFL setting operation thereof of the present embodiment can be applied not only to a digital still camera but also to a digital video camera (movie).

The present invention is not limited to the above-described embodiment, and can be variously modified at the stage of implementation without departing from the scope of the invention. Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some components are deleted from all the components shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effects described in the column of the effect of the invention can be solved. If you get
A configuration from which this configuration requirement is deleted can be extracted as an invention.

[0039]

As described above, according to the present invention,
Various characteristics can be easily evaluated without the need for optical input. Therefore, it is possible to perform blooming characteristic measurement or the like with the imaging apparatus alone without, for example, erroneous determination due to the influence of flare of the optical system.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an imaging device according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a structure of a solid-state imaging device used in the embodiment.

FIG. 3 is an exemplary view showing a cross-sectional structure of the solid-state imaging device used in the embodiment.

FIG. 4 is a circuit diagram showing a structure of a dummy white portion provided in the solid-state imaging device used in the embodiment and a pixel portion of another portion.

FIG. 5 is a diagram showing an example of a current source circuit for flowing a current to a dummy white portion of the solid-state imaging device used in the embodiment.

FIG. 6 is an exemplary flowchart illustrating an overflow level setting operation in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Lens system 102 ... Lens drive mechanism 103 ... Exposure control mechanism 104 ... Filter 105 ... CCD color image sensor 106 ... CCD driver 106a ... VSUB variable setting circuit 107 ... Preprocessing unit 108 ... Digital processing unit 109 ... Card interface 110 ... Memory Card 111 LCD image display system 112 System controller (CPU) 112a Saturation level detection unit 112b Overflow level setting unit 118 Nonvolatile memory (EEPROM) IS IS constant current source

Continued on the front page (72) Inventor Takayuki Kijima 2-43-2 Hatagaya, Shibuya-ku, Tokyo F-term in Olympus Optical Industry Co., Ltd. (reference) 4M118 AA05 AB01 BA13 CA04 DA03 DD09 FA06 FA13 FA26 FA33 GB09 5C024 CX12 CX32 GY24 GZ39

Claims (5)

[Claims] 1. A two-dimensional pixel array in which a charge storage section configured as a pixel in a photoelectric conversion region for photoelectrically converting a subject image is two-dimensionally arranged, and an image pickup for reading out charges stored in the two-dimensional pixel array. Signal reading means;
A pixel portion assigned to at least a part of the two-dimensional pixel array, and a dummy white portion having current source means for inputting a significant charge even when there is no photocharge input to the charge accumulation portion of the pixel. A solid-state imaging device comprising: 2. An optical black OB (optical black) area is provided in the two-dimensional pixel array, and the dummy white portion is provided in an optical black OB (optical black) area in the two-dimensional pixel array. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is provided adjacent to. 3. The device according to claim 1, wherein the dummy white portion is provided at an end of the two-dimensional pixel array.
20. The solid-state imaging device according to claim 20. 4. An imaging apparatus comprising the solid-state imaging device according to claim 1, wherein said solid-state imaging device captures an image of a subject. An imaging apparatus comprising: a saturation level detecting unit configured to detect a saturation level of a photoelectric conversion region of the solid-state imaging device based on an output signal from the unit. 5. An image pickup apparatus comprising the solid-state image pickup device according to claim 2, wherein an image of a subject is picked up using said solid-state image pickup device, wherein an optical black OB (optical black) adjacent to said dummy white portion is provided. An imaging apparatus comprising: means for setting an overflow level of the solid-state imaging device based on an output signal from a region.